SALINITY, ALKALINITY, AND DISSOLVED AND PARTICIPATE ORGANIC CARBON IN THE SACRAMENTO RIVER WATER AT RIO VISTA, CALIFORNIA, AND AT OTHER LOCATIONS IN THE SACRAMENTO-SAN JOAQUIN DELTA, 1980 By Laurence E. Schenel U.S. GEOLOGICAL SURVEY Water Resources Investigations Report 83-4059 Prepared as part of a continuing San Francisco Bay Estuarine study Menlo Park, California 1984 UNITED STATES DEPARTMENT OF THE INTERIOR WILLIAM P. CLARK, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information Copies of this report can write to: be purchased from: Regional Hydrologist Open-File Services Section Water Resources Division Western Distribution Branch U.S. Geological Survey U.S. Geological Survey 345 Middlefield Road Box 25425, Federal Center Menlo Park, CA 94025 Denver, Colorado 80225 Telephone: (303) 234-5888 CONTENTS Page Abs tract 1 Introduction 2 Delta outflow rate and composition estimates -- 2 Seasonal variations in Delta outflow rate 4 Me thods 6 Salinity, dissolved solids, and specific conductance methods and calculations 6 Alkalinity, bicarbonate ion, and dissolved inorganic carbon methods and calculations 7 Dissolved and particulate organic carbon methods 8 Results 8 Mean concentrations and fluxes of solutes and particulate organic carbon at Rio Vista 8 Discussion 10 Concentration variations at Rio Vista 12 Salinity and alkalinity concentration variations 20 Dissolved organic carbon concentration variations 22 Particulate organic carbon concentration variations 23 Summer distributions of solutes in the Delta 25 Summary and conclusions 30 Acknowledgments 30 References 31 Appendix 35 ILLUSTRATIONS Figure 1. Sacramento-San Joaquin Delta 3 2. Average daily estimated Delta outflow during 1980 5 3. Average daily Sacramento River flow at Sacramento and three-day-total precipitation at Sacramento during 1980 13 4. Average daily Sacramento River flow at Sacramento and alkalinity and salinity at Rio Vista during winter of 1980 14 5. Average daily Sacramento River flow at Sacramento and alkalinity and salinity at Rio Vista during spring through fall 1980 16 6. Major tributaries of the Sacramento and San Joaquin Ri ve r s 1 7 7. Sacramento River, Feather River, and American River average daily flows expressed as percentage of the total during spring and summer of 1980 and specific conductance and alkalinity resulting from the mixing of the tributary rivers as calculated from their annual- average concentrations 19 111 Average daily flow from the Glenn-Colusa Irrigation District to the Sacramento River during spring and s umne r 1980 21 9. Dissolved organic carbon concentrations at Rio Vista and three-day-total precipitation at Sacramento duri ng 1980 - 24 10. Particulate organic carbon concentrations at Rio Vista duri ng 1980 - 26 11. Salinity and alkalinity at locations in the main channel of the San Joaquin River and in the southern Delta during July 1980 28 12. Average daily flows of the Sacramento and San Joaquin rivers to the Delta and estimated Delta outflow and total demand during summer 1980 29 Appendix Figure A 44 Figure B 45 TABLES Table 1, Volume weighted average concentrations of dissolved solids (DS), alkalinity (ALK), dissolved organic (DOC), and particulate organic carbon (POC) in near- surface Sacramento River water at Rio Vista, California - Estimated monthly Sacramento River flow and fluxes of dissolved solids (DS), dissolved inorganic carbon (DIG), dissolved organic carbon (DOC) and particulate organic carbon (POC) - 11 Appendix Tables A-E- 36 Metric to Inch-Pound Conversion Table Multiply SI units by_ to obtain inch-pound units kilometer 0.6214 mile me t e r 3.281 feet liter 1.057 quart cubic meter 264.2 gallon cubic meter 35.31 cubic foot per second per second gram 0.03527 ounce IV SALINITY, ALKALINITY, AND DISSOLVED AND PARTICULATE ORGANIC CARBON IN THE SACRAMENTO RIVER WATER AT RIO VISTA, CALIFORNIA, AND AT OTHER LOCATIONS IN THE SACRAMENTO-SAN JOAQUIN DELTA, 1980 By Laurence E. Scheme1 ABSTRACT The salinity, alkalinity, dissolved organic carbon (DOC) and participate organic carbon (POC) concentrations in the Sacramento River water at Rio Vista were measured every 3 to 5 days during 1980 as part of an effort to identify time-dependent variations in the composition of the fresh water flow from the Sacramento-San Joaquin Delta to San Francisco Bay. Concentration ranges were generally small compared to the seasonal range of river flow rate. Thus, transport rates to the Delta and to the Bay varied primarily as a function of flow rate. Even though the tributaries of the Sacramento River are managed by large reservoirs, winter concentration variations are similar to those that have been described in natural unregulated river systems. Because of dilution by surface runoff, salinity and alkalinity are lower when river flow increases during winter storms, whereas DOC and POC concentrations are generally higher during winter. River flow rates and compositions during spring through mid-fall are generally the result of reservoir and water-project management practices. Releases from the major reservoirs on the Sacramento River tributaries resulted in sometimes-large variations in the salinity and alkalinity at Rio Vista. Late summer concentrations were high because of high inflow rates of agricultural waste waters. POC and DOC concentrations varied in response to small storms during spring and late-fall; concentrations were generally lowest during summer. Fresh water inflow from the San Joaquin River increased during late summer, changing the distributions of salinity and alkalinity in the Delta. Salinity and alkalinity were highest in the east Delta during early summer. Higher flows and decreased water project demands during late summer decreased salinity and alkalinity in the east Delta, while salinity and alkalinity increased in the west Delta due to the influences of agricultural waste water inflows. INTRODUCTION Fresh water from the Sacramento-San Joaquin River Delta (Delta outflow) constitutes about 90 percent of the total annual fresh water flow to San Fran­ cisco Bay and accounts for most of the transport of riverine dissolved and particulate substances to the Bay (see Conomos 1979 for a summary of the hydrol­ ogy of San Francisco Bay; Conomos and others 1979). Interdisciplinary field studies of the Bay estuarine system conducted by the U.S. Geological Survey during 1980 required estimates of riverine transports to the Bay and measure­ ments of time-dependent variations in Delta outflow composition. As part of this effort, Sacramento River water was sampled every 2 to 5 days at Rio Vista and Delta waters at other locations were sampled 3 times during summer (fig. 1; appendix table A). Samples were analyzed for salinity (electrical conductance), alkalinity, and dissolved and particulate organic carbon (DOC and POC, respec­ tively). This report presents 1) the numerical values for these analyses, 2) estimates of the transports of these substances by the Sacramento River, 3) plots of the results that illustrate seasonal variations in composition, and A) a descriptive interpretation of the results that identifies the most prob­ able causes for Delta outflow composition variations. Delta Outflow Rate and Composition Estimates The rate of Delta outflow to the Bay cannot be directly measured and, similarly, the composition of the Delta outflow cannot be determined by sampling at any one location over the entire hydrologic year. The accuracies of transport estimates are limited by the potentially large uncertainties in the Delta outflow rate and composition estimates. Estimates of Delta outflow rate are based on the river flow rates to the Delta (Delta inflow) and the sum of the consumption in the Delta and export to State and Federal water projects (total demand). The Delta outflow index (DOI) is a daily estimate prepared by the U.S. Bureau of Reclamation (USER), that accounts for the flows of the major river systems (Sacramento and San Joaquin) and the total demand. A more accu­ rate estimate can be prepared by adding the flows of four smaller rivers that enter the east side of the Delta (east-side rivers) and the flow that is divert­ ed from the Sacramento River to the Yolo Bypass (fig. 1) during winter (Janu­ ary through March). This diversion prevents flooding in the Sacramento metropolitan area; the water returns to the Sacramento River upstream of Rio Vista. The flows from the east side rivers and Yolo Bypass were 5 and 18 percent, respectively, of the total Delta inflow during 1980. The Sacramento River flow rates given in this report include the flow rates to the Yolo Bypass. Because the flow from the Yolo Bypass to the Sacramento River is not measured, it must be assumed that the return flow is the same as the diverted flow. According to State of California water-supply criteria, 1980 is con­ sidered a "wet" year. The total Delta inflow was 3.9 x 1010m3 and the total Delta outflow was 3.2 x 1010m 3 (U.S. Geological Survey 1981a; a monthly 121°45' Slow ^=^ycamore^Sloiigli r^ Terminous Figure 1. Sacramento-San Joaquin River Delta. Bridge sampling locations are shown by dots. Base taken from U.S.Army Map Service 1:250,000 maps numbers NJ 10-5, NJ10-6, NJ 10-8, and NJ 10-9. summary of Delta inflows and outflows Is given in appendix table B). The Sacramento River is the largest source of fresh water to the Delta, contribut­ ing 76 percent of the total Delta inflow during 1980. The second largest river, the San Joaquin, contributed only 19 percent of the 1980 Delta inflow. In addition to the significance of its large annual discharge, the Sacramento River delivers water to the west Delta and therefore contributes an even larger fraction of the flow to the Bay during most times of the year. Thus, it is probable that the composition of the Sacramento Piver water closely approximates the Delta outflow composition. The Rio Vista bridge was selected as the sampling location because it is downstream of where flow from the Yolo Bypass rejoins the Sacramento River and because brackish water, that is drawn into the Delta during periods of low Delta outflow, rarely extends to Rio Vista.